Crop rotation theory v. practice

Question

Every guide to growing vegetables will have an early section on rotating roots, brassicas and legumes. There might even be a little diagram with neat evenly spaced and sized areas marked out for each group.

It always sounds so simple in theory.

But the guides are frustratingly silent on practical questions.

1. What if you don't tend to grow the three groups in even quantities (say you grow very few brassicas)?

2. What if your vegetable plot isn't uniform in its distribution of warmth, light and soil quality? For example I always want to start off early salads, radishes and carrots up the warm end of my little rectangle in Feb/Mar. But that's crop rotation immediately messed up.

3. Where do salads fit in?

Answer 1

I've been trending towards lots of heavily interspersed companion gardening (e.g. rather than 10ft of onions and 10 ft of carrots, I'll have 1ft of onions, and 1ft of carrots, ten times). And I like to completely change up my garden layout from one year to the next. So the chance of any particular crop being grown in the same place two years in a row is slim, even if I don't put any mental energy into planning the rotation.

Likewise, I try to make sure that new compost gets laid down at least once a year. And definitely think about fall/winter cover crops that might nourish the soil.

So I take the roots/brassica/legume as one guideline among many. Another guideline I've read is squash => nightshades => grains (corn) => beans. Or nightshades/potatoes => brassica => carrots => alliums. Or three years of anything and then legumes. These are good guidelines, but as a home gardener don't stress yourself out over them.

Since salads tend to be spring/fall crops, I'll either rotate them with turnips/radishes, or I'll rotate which parts of the garden are used for spring or summer crops. I have one area of my garden that gets great light in the early spring, but only about 5-6hrs of direct sun during the late spring through fall. So I tend to rotate quick spring veggies (e.g. lettuce), root veggies, alliums, and herbs through there, because that's what will grow there.

The point is that there are different crop rotation recommendations, but you can relax them a bit if you put down fresh compost every fall and spring, keep things moving around so the soil doesn't get too stressed, and make sure those nitrogen fixers get a chance at every spot in your garden every so often. It's all about the health of the soil.

Answer 2

(thinks back to my UK high school "Agricultural Revolution" classes) One of the many advancements in agriculture was the change from a three course rotation (crop,crop,fallow) to a "Norfolk Four Course" (three crops, and a legume). The idea of the legume is that it is a nitrogen fixer - basically growing the legume crop also adds nitrogen to the soil. Free fertilizer! So choose a legume that suits your growing conditions and what you would like to eat. I've only really tried it with black beans - but they're something I could eat as much as I could grow.

So I think it can be a lot more flexible than what you are thinking. It doesn't have to be a strict rotation, but alternate your crops so that each plot grows legumes at some point every 3-4 years.

The other reason I can think of, where rotation could be useful is to try and keep pest levels down. E.g. diseases could theoretically build up in the soil if you plant the same crop every year. A little bit might not be a problem one year, but the next year the pest might thrive as it has its ideal food in the same spot. Rotating the crops helps to confuse them. Also growing crops together in alternate rows can help (eg. the English trick of growing onions and carrots together: the onion scent confuses the carrot fly).

Answer 3

Another reason for crop rotation, I believe, is that nutritional needs and intake vary slightly from one vegetable group to another; therefore, growing the same group on the same plot year after year may deplete the soil of a particular nutrient and lead to unhealthy crops.

Answer 4

I agree with winwaed that it doesn't have to be a strict rotation.

One other thing you could consider is the various "Green manure" crops. If you are having trouble working out what comes next on a bed, or don't really want legumes - then green manure is normally cheap (at least in bulk), improves the soil and will help keep weeds down in an otherwise quiet time on your plots.

You can also use Green Manure as part of the rotation ("green manure" is a term used for crops that grow well, can crowd out weeds and decompose easily). This appears to be a contentious subject though. Using as suggested here is fine... but you might be better growing something "real" - even if only to give the produce away.

Answer 5

In "The New Organic Grower", Eliot Coleman describes a real-world approach to crop rotation. (There's a full chapter on it.) He works through an example of a theoretical 10-year rotation, and discusses the real-world 8-year rotation he's been using for a couple of decades. You could scale it back to 3 or 4 year if you wanted to.

First, divide up your crops into groups along two or three different axes: botanical family, cultural requirements, space required, etc. Note that you will have crops that land in different groups -- turnips+carrots will be together in a "root veg" group, but turnips+broccoli will be together in the "brassica" group.

Then decide how many rotations you're going to have and get that many index cards (or scraps of paper).

Create your rotation groups by putting together the vegetables you're going to grow together. Use some of the groupings you created above to guide you regarding which to put together since they share cultural requirements (planting in spring in the warm end; but see below too). Using the example from your question, you'd put salads, radishes and carrots on one card. Since you grow very few brassicas, you may put brassicas on a card with your herbs and onions. (I'm just making up a -- possibly poor -- example, assuming this will fill up the space allocated to a rotation.)

Shuffle your cards around until you have a good set of preceding crops. E.g. perhaps you want your peas before your brassicas because you've seen that peas help brassicas and onions. Or (using an example from the book) you put potatoes, then squash, then roots -- because the culture applied to potatoes and squash reduces weed pressure, and root vegetables don't handle weed pressure well.

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Be willing to experiment. In my garden I've used a 5-year rotation, but I'm going to adopt a 7-year rotation starting next spring. I also want to shuffle around some of the sequences I have -- for example, I've learned that it is rather inconvenient to have cucumbers located next to tomatoes. Two space-hogs sharing space makes harvesting a hassle.

The uneven distribution of light is a hard thing to fix. Maybe you can't fix it. And maybe it doesn't matter -- experimenting a bit will help you find out.

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Consider green manures and fallow periods. Coleman also discusses this in a chapter of the book. As part of my 7-year rotation, I'm planning on leaving about 1/4 to 1/3 of the space to a green manure for a year at a time. (I'm starting red clover late this summer that will grow in that spot all next summer and get turned under next fall.) This is an excellent path to soil building. (He also discusses -- and I'm considering -- pasturing chickens and/or sheep on the area to add fertility, but that's out of scope for most people on this site.)

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As far as an uneven distribution of warmth and soil quality goes, part of the point of the rotation is to give you a chance to even these out. Use the rotation to improve the soil quality in year 1 for the crop that will grow there in year 2. E.g. plant peas to add nitrogen for the following crop of brassicas, and be sure to capture the nitrogen using a cover crop of winter rye that you sow immediately after removing the peas.

You can help the soil warm up in spring by doing certain things in the fall. Forage radish, for example, will winter-kill, leaving holes in the soil. These are supposed to dry out and warm up earlier in the spring. If you normally spread a heavy mulch, or plant a thick winter cover crop, don't do that before the "plant in early spring" part of the rotation -- it delays soil warming. If you normally plant "on the flat", then in the fall mound up some beds for planting into in the spring -- these will warm up faster.

Answer 6

Some crops actually prefer to be planted in the same place every year. (i.e. Nightshade family [tomatoes, potatoes etc..]).

Three rotations is a bit much for me, and probably most other Wisconsin gardeners. I can usually do radishes and then zucchini; spinach and then kale (not a good rotation, but a practical one); peas and then cucumbers.

But companion planting seems much more suitable, fun, functional, verdant and beautiful. You can get the full benefit of crop rotation, without the wait and uncertainty.

No garden is uniform (except my grandpa's, who grew his on an old dump full of leaves, slag and manufacturers glass) and there's something like 20,000 different types of soil which would mean that it might not even be efficient or wise to rotate your crops if they do better in different parts of your garden.